PSI - Issue 18

Luigi Mario Viespoli et al. / Procedia Structural Integrity 18 (2019) 86–92 Author name / Structural Integrity Procedia 00 (2019) 000–000

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predominant it would be necessary to produce new results for the material in condition of different grain size, assessing then the value of the exponent q.

Fig. 3. Longitudinal DIC strain obtained in the step test. The numbers indicate the steps, *9 being the relaxation step.

Figure 4. Steady state creep regimes and relative exponents as obtained from the analysis of the step test points in positive stress, plus the results of the tensile testing in which constant stress is reached. 4. Conclusions The present work is the synthesis of a series of tests on dog-bone specimens of a lead E alloy industrially used for the production of the sheathing layer of subsea power cables. Firstly, the three tests at different nominal strain rates plus a relaxation test were performed to characterize the strain rate sensitivity caused by the creep mechanisms active and to calibrate the parameters of a numerical model based on the Anand creep model, which successfully approximated the mechanical response of the alloy to the deformation imposed. To study the mechanisms active during the time dependent deformation of the alloy the steady state creep behavior was investigated. From the results of a tensile test composed of several steps at different stress levels, each of which reached the secondary creep stage, the exponent correlating stress and strain rate for steady state creep was obtained between 3 and 12 MPa. The values assumed by such material parameter in the range of interest indicate that mechanisms of diffusional creep are active in the low stress range of 3 to 5 MPa, with a value of the exponent close to 1, while dislocation creep is the dominating mechanism for higher stresses, with values ranging from 5.5 to 8.4. Further testing for different average grain size would then be necessary in the low stress range to determine whether vacancy diffusion through the crystal lattice or vacancy diffusion along the grain boundaries is predominant.